Grid cathode assembly for cathoderay tubes



June 6, i950 w, J, ToLsoN 2,510,257

GRID CATHODE ASSEMBLY FOR CATHODE-RAY TUBES Filed OGl. 50, 1946 l f..........f 'l l l 74\ i1/5 il; s, 4 j m MT L L l c 7./ -63 :inventor E www forward into the :tube envelope.

Patented June 6, 1950 "Wilsonl Tolson, Lancaster,y Pa., assignorto Radio Corporation of "America,'a corporation of "Delaware Application october 30, 1946,' seriai'No. "zcoo 12 Claims.

My invention relates to'cathode ray tubes, and in particular to a cathode'grid unit assembly for such tubes. v l n M v o YIn a conventional'ty'pe of 'cathode raytube a "catho/'de emittingelectrode' is axially aligned with LtheV apertures in a pluralitylof platesor grids. :Inf the type of cathode jray`tube of which this "invention is an improvement, electronV emission from the cathodepasses'inturnthrougha control `gridplate, a focusinggrid plate, a first/'anode accelerating cylinder andwa second anode grid plate. The spacing between theemitting surface ofthe cathode andthe cotrolegrid is very critical. v v o l o 1 In the past,'spacers`have been'usedto hold the cathode emitting fwsurface at a predetermined v'distance from the control grid. These spacers have Ftaken the fform of metal Vveyelets and annular ceramic insulators, lor rthe lilv e. v There Y are several objectionsto the use of spacers. Where several tube types are Arproduced VKeach requiring a different cathode-gridspacing;it'is necessary to stock a'large number'of dfferentsize spacers. Also, as the cathode-grid distance is critical the spacer must 'closelyc'onformby a small tolerance tothe predetermined' distance. This requirement necessitates Yprecise work and close'inspection for each metal or ceramic spacer, y

"conventionally, the vcatlfiode'tube or sleeve is coaxially supported by an annular ceramic disc mounted within thevgrid cylinder. Change in grid-cathode spacing is dueto the expanding of the hot'cathode sleeve when the'heater is turned on. This' isdueto the "metal of the 'cathode sleeve pushingaway from the ceramic `disctoward`the grid aperture. v v Y Y Also, in 'a conventional type of electron gun 'for cathode ray tubes.thecathodeis'open at the flower end to provide 'a passagefor filamentvleads extending upward from the tube stem. This arrangement permits light 'from 'the filament to shine through the open end of the cathode upon Ithe upper'surface ofthe glass stern. This light is reflected vfrom the surface of the glass y'stem 4 n Part of the reflected light 'falls upon the fiur'escent target of the tube and `tends tofrnasky the signal. This result is particularly undesirable, for example, in aircraft radar receivers using cathoderay tubes in which faint signals would'be hidden by the reflected light.

Itis. therefore, 'an object of my 'invention to provide a cathode Jray tube having an improved electrode construction. l 1

Anotherobjectof my'invention is to provide a grid-'cathode construction having'accurate Vgridcathode spacing. v o Y It is also'an'object of 'my'invention toprovide a grid-cathode unit having la novel construction resulting in cheaper, quicker anda 'simplified assembly. Y l v v i Y 4It isalsoan object of nfyinvention to provide a grid-cathode unity construction which is Vassembled' of parts madeto geater'tolerances, yet withacatho'de to grid vspacing conforming more closely to ai predetermined distance. v

lIt is Valso an object of my invention to provide ak grid-cathode vassembly which prevents the transmission" of 4lariert light.

Itis also anob'ject of my invention to provide a novel cathodegrd assembly which shortens the overall length of the electron gun.

The novel features Vwhich I believeto be characteristic of my inventionare setforth with particularity in the appendedclaims, but the invention itself will best beunderstoodby reference to the following 'description taken lin connection withthe accompanying 'drawinggin which:

Fig. l is an elevational view partlydn'section of a cathode ray 4tube 'incorporatingthe cathode construction according' to my invention;

Fig. 2 is an elevational view 4in section of a cathode assembly according'to my invention; and Fig. I3 is an exploded elevational'view section of a cathode-assembly according 'to a modification of my invention. Y v

My invention is directed principally to improvements in a cathode grid-assembly for use in a cathode ray tube. Such a cathode ray tube is disclosed in Fig. 1 as having an envelope I 0 closed at one end by'a glass stem portion 26 hermetically sealed to the sides of the envelope Vl il. Mounted upon the glass stem 2tv is an electron beam-forming structure supported principally by ceramicside rods |I. Mounted on the side rods il and fixed relatively thereto is a cathode-grid assembly I2 for providing a source of an electron beam vwhich is focused through a second grid structure i4 'axially spaced along the tube from the cathode-grid assembly. Spaced in turn from 'the second grid I4 along the axis of the tube are a first anode I6, a second anodeml and pairs of deflecting 'plates 20 and 22. These several structures form, focus and accelerate the electron beam in a manner'w'ell known in the art to strike the fluorescent screen 24. A

The cathode-grid assembly is disclosed in greater detail in Figs. 2 and 3.` The assembly. l2 comprises, first, a container portion of cylindrical parts ti) and 42. The 4cylindrical parts are of diierent dimensions and are coaxially joined together by an annular shoulder portion 44. The grid body 49-42 may be formed in` any manner that is expedient such as machining or by drawing. The cylindrical part 49 having a smaller cross-sectional diameter is closed at one end by a plate portion 45 having an aperture 46 coaxial with the cylindrical part 49. The cylindrical part 42 is provided with an aperture or opening 43 in the side wall thereof as shown in Figs. 1 andv 2. Mounted within the cylindrical portions 49 and 42 is a cathode structure or assembly 49, comprising an outer supporting cylinder or tube 59 iixed to a support eyelet or tube 56. The support eyelet 59 is flanged at its lower end to provide an outwardly projecting part 58. Welded to the outer surface of the support eyelet or tube 55 is an annular shield 69. ceramic spacer disc or annular plate 92 is mounted over the support eyelet or tube 59 and rigidly held between the flanged portion 58 and the annular shield ring 69. The vouter support cylinder 59 is made of very thin metal foil preferably of a nickel-iron-cobalt alloy which has a low heat conductivity. Covering the upper portion of the supporting cylinder or tube 59 is a cathode cap 52 fixed at its edges to the support cylinder 59. The top portion of the cap 52 may be covered with an electron emitting material as is well known in the art. Fixed to the inner portion of the support cylinder or tube Y59 is an inner cathode eyelet or tube 54 supported at its top end and extendingdownwards and coaxial with the cathode structure. The lower end of the inner cathode eyelet 54 is unsupported and spaced from the rest of the cathode structure.

The cathode assembly 49 is mounted within the grid body by securing the ceramic spacer 92 of the cathode structure between the shoulder portion 44 of the grid body and an end shield plate 68. Between the shield plate 68 and the ceramic washer 62 are placed two ceramic spacers or annular insulators 64 and B6. annular shield 68 is fitted into the open end of the cylindrical portion 42 and forced against the ceramic insulators to a position where it is fixed by welding or brazing to the sides of the cylindrical portion 42. In this manner the cathode assembly 49 is rigidly mounted within the grid body lin- 42, with the cap or tube portion 52 spaced from the apertured end plate 45.

Fig. 3 shows a modification of the grid body which comprises a single cylindrical portion or tube 'l5 closed at one end `by a plate portion 18 having an aperturetherethrough coaxial with the cylinder '56. At the open end of the cylinder l5 an aperture or opening 82 is formed through the side wall. Fixed within the cylinder 19 is .an annular flanged ring `84 mounted by welding or brazing, for example, to the side wall of the cylinder i6 in a predetermined position. The annular ring 84 is provided with-a. flanged portion 86 against which abuts the supporting ceramic spacer 62 of the cathode assembly 49.

In Fig. 3 the cathode assembly 49 may be iixed within the-grid body l in a manner similar to that shown in Fig. 2 in which the cathode assembly is locked by the plate 69. The cathode structure disclosed in Figs. 2 and 3 is of the indirectly heated type. In Fig. 2 is disclosed a lament 12 which may be of the double helical type extending inside the cathode assembly. The filament 12 is completely enclosed by the inner cathode eyelet or tube 54 and the cathode cap portion 52. The ends of the filament are brought down A supporting through the apertured spacers 64 and 69 where they are mounted -for support on two lament leads 74. Leads 14 extend into the grid body through the aperture 43 and between the ceramic spacers 94 and 66. They are frictionally held in position by the pressure exerted between the annular shield 68 and the shoulder 44 of the grid body. Filament leads 14 are of sufficient rigidity to be capable of supporting the filament 12. The cathode is furnished with an electrical lead 19 which also extends into the grid body through the opening 43. The lead 19 is frictionally held or pinched between the ceramic support 92 and the spacer 64. It is Welded at 'H to the annular flange 58 of the cathode sleeve structure.

During tube operation, the incandescent filament l2 heats the cathode cap 52 to a temperature sufiicient to cause electron emission from the activated coating on the surface of the cap. During normal tube operation there is a sputtering of emissive material from the cathode cap onto adjacent portions of the cathode grid structure. To prevent shorting between the grid body 49 and the cathode 49, shield 99 extends out over the ceramic supporting insulator 62. As shown in Figures 2 and 3, the peripheral portions of shield 69 are spaced from the upper surface of the insulator 62. This prevents any of the sputtered material from being deposited upon the ceramic 92 and thus prevents the formation of an electrical path between the grid body 49 and the cathode assembly 49.

In cathode ray tubes of this type, the spacing between the cathode emitting surface and the iirst grid is very critical. The amount of the spacing is usually Very small, varying in di'erent tubes all the way from 5 mils to 20 mils. Furthermore, the tolerance allowed for this spacing is usually l to 2 mils either way. To conform to such close tolerance and to maintain the reouired spacing has proved Very difcult. The problems of manufacturing are multiplied when these gridcethode assemblies are made in large amounts. Previously, construction of the cathode grid assembly has required accurately formed elements whose dimensions vary, if any, by a Very little. Furthermore, during the assembling of the cathode grid structure close inspection must be continually made to check any variation in structure of one assembly from another.

In my invention, however, I have devised an arrangement of parts from which many of the diiculties of the past have been eliminated.

Fig. 3 shows several sub-assemblies, the grid body 16, the cathode sleeve unit 55 and the cathode support assembly 59. To assemble these several sub-assemblies so as to provide an accurate spacing between the cathode cap 52 and the apertured grid plate 'I8 the following procedure may be used.

The cathode support assembly 59 is held by an appropriate jig mechanism (not shown). The cathode sleeve unit 55 is slipped over the support assembly 59 so that support cylinder 59 telescopingly ts over the support eyelet 5B. The spacer 95 is next fitted on the top of cap 52. The grid body 'l5 is placed over these assembled units so that the lower open end of the grid body 'I6 slips down over the ceramic spacer 92. A suitable press means (not shown) forces the grid body 1E and the support assembly 59 together until the ceramic B2 :abuts against the flange 89. The grid body 19 and assembly 59 are held in this position while a plunger means within the .jig is moved up through support eyelet or tube 56 and cathode eyelet or tube 54 to contact the inner surface of cap 52. The motion of the plunger is continued to carry the cathode assembly upward until the spacer 94 abuts against the inner surface of the grid plate 18. The cathode emitting surface 52 is now accurately spaced from the grid plate 18, while the grid unit 55 and the support assembly 59 are accurately positioned with relation to each other. Means are provided to lock the sub-assemblies 55 and 59 together in this relationship, while the grid body 16 is removed, then tubular sleeves 50 and 55 are welded together and spacer 94 removed from the cap 52.

With the two portions 55 and 59 of the cathode structure now welded together in the desired relationship the cathode-grid unit i2 may be assembled by any desirable means. The cathode assembly l55--59, without spacer 94, is inserted `into the grid body 16. The two ceramic `spacers 64 and 66 are inserted in turn. Leads 14 are `positioned between spacers 64, 66 and filament 12 is then mounted within sleeve 54 on the ends of `leads 14. The cathode assembly 55-59 and the spacers then are locked within the grid body 16 with the welding of the shield plate 68 to the wall ofthe grid body 16. This is done in `such a manner that the ceramic spacers 62, 64 and 69 are held under pressure between the shield ring 6B and the flanged ring 84.

The advantages of this particular method of assembling the cathode grid structure are many. In the conventional type of cathode structurethe cathode comprises of a simple cylinder supported by an annular ceramic disc which is fixed tothe cathode cylinder between two flanged portions thereof. This cathode cylinder is spaced by a vmetal or a ceramic spacing means from the grid aperture. One common form of spacer is that of a metal eyelet between the apertured-end plate of the grid body and the ceramic spacer.

In a conventional grid cathode assembly of this type the spacingbetween the cathode surface and kthe apertured grid plate is governed by the axial dimensions of the cer-amic or metal spacer between the cathode unit and the grid plate. This part must be made to a predetermined axial dimension and within very small tolerances. Great difficulty has been experienced in providing support ceramics and spacer eyelets of the required axial dimension. Such difliculties :are those of time consumed in checking and inspecting the component parts to determine whether they conform to the required dimensions. Such a nrocedure of cathode grid assembly has proved rather wasteful due to the discarding of many parts which do not come up to the exact standards required. Another difficulty has been in the making of sever-al cathode grid structures in each of which there is a diiferent rcathode to grid spacing. In such cases it is necessary tc stock spacer eyelets or ceramics of different sizes.

In the particular structure of my cathode an-d the method of assembly disclosed above, many of these difficulties do not appear or are eliminated. All that is required to make grid cathode assemblies having different spacings is the provision of a plurality of spacers one for each of grid-to-cathode spacing required. Furthermore, it is easily seen that with my particular cathode structure the axial dimension of the several cornponent parts does not have to be critical. Tha-t is, the spacing between the cathode surface an-d the grid plate does not depend upon an accurate determination of the axial dimensions of any of the cathode parts. 'I'he spacing is determined entirely by the spacer 94 and the parts are so designed that any reasonable variation in the axial dimension of any'of the essential parts such as support ceramic 62, the support cylinder or tube 56 or the outer support cylinder or tube 59 will not affect the grid-cathode spacing. Furthermore, time consuming inspection of parts is eliminated.

A cathode grid vassembly as disclosed Vin Figs. 1 and 2 has several other distinct advantages. In cathode ray tubes it is desirable to have the overall length of the tube as short as possible for reasons of installation. My particular cathode grid structure allows the mounting of the cathode gun structure closer to the glass stem of the tube. This is provided by the vfact that the filament leads 14 and the cathode lead 19 pass through the side of the grid body. This arrangement is in contrast to the conventional method in which the'cathode grid body is completely open at the lower end and the filament leads and cathode leads extend out through this open end. My arrangement allows the `cathode grid structure to be supported closer to the tube stem 26.

Another great disadvantage of the conventional cathode grid assembly is that the open end of the grid assembly permits light from the filament to shine down upon the glass surface of the tube stem. This lament light is reflected from the surface of the glass stem forward upon the fluorescent screen `at the opposite end of the tube. The phosphor of the screen glows Vfrom this reflected light and tends to mask or hide signals produced on the fluorescent screen bythe electron beam. Ihis phenomenon has provided somewhat of a problem in aircraft radar kine-scopes. In radar work many faint signals are picked up and these signals :are completely hidden by the glow due to the reected light. To eliminate this particular difficulty I have` completely closed off the bottom end of my cathode grid structure with the plate 68. This provides a grid body which completely encloses a cathode structure in such a way as to vscreen any incandescent part of the cathode assembly.

The particular structure of the cathode components described in Figs. 2 and 3 possesses still another advantage. To maintain the cathode to grid spacing during normal tube operation has oftentimes proved to be a problem. In the conventional type of cathode structure described above, the high temperatures which the cathode structures attain cause an expansion of the cathode sleeve and if spacers are used between the cathode and the grid end plate these high temperatures cause a change in the diamensions of the spacers and a tendency for the end plate on the cathode structure to warp. This last problem has been eliminated in my structure with the elimination of the spacerrelements.

In my cathode, the radiated heat from the la- 4ment is absorbed by sleeve 54 and conducted to the cathode cap 52 by this sleeve or im1 er cathode eyelet 54. Furthermore, the cylinder 5d being of a very thin metal foil and also bei-ng of a low heat conducting alloy prevents escape of heat from the cap 52 to other parts of cathode structure. If any axial expansion of the cathode takes place it will mostly be in the highly heated inner eyelet 54. Since the lower end of this eyellet is unsupported all expansion will take place in a rdownward direction so that the cathode to grid spacing is maintained.

While certain specific embodiments have `been 'illustrated and described, it will kbe understood that various changes and modications may be made therein without departing from the spirit and scope of the invention. What I claim as new is: 1. A cathode electrode unit comprising a tube, -deans closing one end of said tube, means including a shield xed to and projecting laterally from the surface of said tube, and a support member mounted on said tube and fixed in position be tween said shield and another of said projecting means, the peripheral portion of said shield being spaced from the surface of said supporting member.

2. A cathode electrode unit comprising a tube, means closing one end of said tube, means including a shield fixed to and projecting laterally from the surface of said tube, and an annular insulator member coaxially mounted on said tube and xed in position between said shield and another of said projecting means, the peripheral portion of said shield being spaced from the surface of said insulating member.

3. A cathode electrode unit comprising a hollow tube, means closing one end of said tube, the other end of said tube having a flange portion extending outwardly therefrom, a support mounted with one surface in abutment against said flange portion, a shield means iixedly mounted on said tube in contact with an opposite surface of said support, whereby said insulator support is locked to said tube between said dan ge portion and said shield means.

4. A cathode electrode unit comprising a hollow tube, means closing one end of said tube. the

other end of said tube having a flange portion extending outwardly therefrom, an insulator coaxially mounted with one face in abutment against said ange portion, and an annular shield fixedly mounted on the outer surface off do said tube in contact with an opposite face of said insulator, whereby said insulator is locked to said tube between said iiange portion and said annular shield.

5. A cathode electrode comprising a tube,y

means including an electron emitter surface closing one end of said tube, the other end of said tube having a portion extending outwardly therefrom, a shield mounted on the outer surface of said tube and spaced from said outwardly ex-v other end of said tubular portion and held in fixed relationship by said flange and said annular shield.

7. A cathode grid assembly unit comprising a grid body having two cylindrical wall portions of different diameters coaxially joined end to end by an annular wall portion, said annular wall portion partially closing said end of the larger cylindrical portion, a wall having an aperture at its center closing the other end of the vsmaller cylindrical portion, a shielding plate fixed to the inner wall of said larger cylindrical portion and closing the other end thereof, an `insulating support member clamped between said annular wall portion and said shielding plate, a cathode tube xedly mounted at one end to said insulating support member, the other end of said cathode tube extending coaxially into said smaller cylindrical portion and havin-g an electron emitting surface spaced from said apertured wall.

8. A cathode grid assembly unit comprising a grid body having two cylindrical wall portions respectively of diiferent diameters coaxially joined end to end by an annular wall portion, Sad annular wall portion partially closing said. end of the larger cylindrical portion, a wall having an aperture at its center closing the other end of the smaller cylindrical portion, a shielding plate xed to the inner wall of said larger cylindrical portion and closing the other end thereof, said larger cylindrical portion having an aperture in the side wall thereof, an insulating support member and an annular spacer Adisc clamped side by side between said annular wall portion and said shielding plate, a cathode tube iixedly mounted at one end to said insulating Support member, the other end of said cathode tube extending coaxially into said smaller cylindrical portion and having an electron emitting surface spaced from said apertured wall, a cathode lead xecl to said cathode tube and extending between said insulating support member and said spacer disc through said aperture yin the side wall.

9. A cathode grid assembly unit comprising a grid body including two hollow cylindrical portions of different inside diameters, an `'annular portion coaxially joining said cylindrical portions together end to end, a wall portion closing the other end of said smaller cylindrical portion and having an aperture coaxially thereto, said larger cylindrical portion having an aperture in the cylindrical wall thereof, a cathode electrode unit including an electron emitting tube having an elec-tron emitting surface at one end thereof and an annular insulating support iixedly mounted coaxially on said emitting tube at its other end, said cathode electrode unit mounted with the electron emitting surface of said tube extending coaxially into said smaller cylindrical portion in spaced relationship to said apertured wall and said annular insulating support in abutment with said annular portion, a pair oi annular insulating spacer discs coaxially positioned side by side against said insulating support, and a circular plate shield closing the other end of said larger cylinder and fixed to said larger cylinder, said annular insulating support and said pair of spacer discs clamped together between said plate shield and said annular portion, a cathode electrode lead fixed to said cathode tube and extending through said aperture in the cylindrical wall of said larger cylinder, a pair of spaced cathode filament leads held between said pair of insulating spacers with one end oi said filament leads extending into the apertured center of said insulating spacers, a cathode filament mounted on said one `end of said lament leads and extending into said cathode tube, the other end of said filament leads ,extending through said aperture in the wall of said larger Vcylindrical portion.

l0. A cathode grid assembly unit comprising a grid body having two cylindrical wall portions of different diameters and an annu-lar wall portion joining said cylindrical wall portions, a shielding plate fixed -to the inner wall of the larger cylindrical portion and closing one end thereof, an insulating support member clamped between said annular wall portion and said shielding plate, a cathode tube xedly mounted at one end to said insulating support member, the other end of said cathode tube extending coaxially into said smaller cylindrical portion.

l1. A cathode grid assembly unit comprising a grid body including a hollow tubular member, stop means projecting from the inner surface of said tubular member, a tubular cathode electrode unit having an electron emitting surface at one end thereof, an insulator xedly mounted on said tubular cathode unit at its other end, said cathode electrode unit mounted with the electron emitting surface extending into said tubular member with said insulator in abutment with said stop means, means closing the other end of said tube, said insulator clamped between said closing means and said stop means.

12. A cathode grid assembly unit comprising a grid body including a hollow tubular member, stop means projecting from the inner surface of said tubular member, said tubular member having an aperture in the wall thereof, a tubular cathode electrode unit having an electron emitting surface at one end thereof, an insulator xedly mounted on said tubular cathode unit at its other end, said cathode electrode unit mounted with the electron emitting surface extending into said tubular member with said insulator in abutment with said stop means, means closing the other end of said tube, said insulator clamped between said closing means and said stop means, a cathode electrode lead xed to said cathode electrode and extending through said aperture in the wall of said tube.

WILSON J. TOLSON.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,244,358 Ewald June 3, 1941 2,386,790 Gaun et al Oct. 16, 1945 2,406,850 Pierce Sept. 3, 1946 

